This invention relates to a device for the centered clamping of annular workpieces, particularly resilient piston rings, to position them for machining operations to be performed on the internal faces thereof. The device includes two clamping rings adapted to engage, on opposite radial sides, the piston ring or, as the case may be, the piston ring stack, a mechanism to urge the clamping rings axially towards one another and a centering cylinder which surrounds the piston rings and which is provided with a chamfered lead-in edge.
Arrangements for the clamping of a single ring or a ring stack between annular clamping bodies engaging opposite radial sides of the ring(s) to position the latter for performing machining operations on the external or internal circumferential ring faces are generally known. For the centering of the radially resilient piston rings either rigid centering cylinders with a conical (chamfered) lead-in edge (as disclosed, for example, in German Pat. No. 1,014,410) or radially adjustable centering devices (as disclosed, for example, in U.S. Pat. No. 1,897,397) are used.
In German laid-open application (Offenlegungsschrift) No. 2,144,800 there is disclosed a device for the internal machining of piston rings wherein the piston rings are pressed axially into a stationary centering cylinder (having an axial abutment) to thus position the rings for machining the inner circumferential ring surfaces by means of a rotating tool. Additional, resiliently supported ejecting pins are provided for the axial discharge of the piston rings upon completion of the machining. It is a disadvantage of a device of this type that only small-diameter piston rings may be efficiently machined, because the imbalance of the rotating tool is too high in case of large-diameter piston rings and thus the turning tool may not be operated with the maximum cutting speed. It is a further advantage of this device that it is designed for a particular machining operation and cannot be used for other purposes.
The clamping device disclosed in German Pat. No. 1,104,410, on the other hand, may be mounted on any conventional machine tool such as a lathe. While the device disclosed in this German Patent is designed exclusively to position piston rings for an external machining, the device disclosed in German Pat. No. 571,579 may be utilized for both an external and a successive internal machining of the piston rings. In this known structure the axial clamping of the piston ring stack is effected exclusively manually by means of a centrally extending tensioning bolt or at least two tensioning bolts which extend externally of the piston ring stack.